Method of forming isolation layer

ABSTRACT

According to an exemplary embodiment, a method of forming an isolation layer is provided. The method includes the following operations: providing a substrate; providing a vertical structure having a first layer over the substrate; providing a first interlayer dielectric over the first layer; performing CMP on the first interlayer dielectric; and etching back the first interlayer dielectric and the first layer to form the isolation layer corresponding to a source of the vertical structure.

RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No. 16/049,520, filed on Jul. 30, 2018, which is a Divisional of U.S. patent application Ser. No. 14/303,791, filed on Jun. 13, 2014, now U.S. Pat. No. 10,418,271, the disclosures of which applications are incorporated herein by reference

BACKGROUND

Vertical semiconductor devices, such as vertical gate-all-around transistors, are an emerging research area in the semiconductor industry. However, low pattern density of the vertical semiconductor devices may weaken thickness uniformity control of inter-layer dielectrics (or isolation layer) therein. Therefore, there is a need to improve the above deficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1-11 are sectional views illustrating an exemplary semiconductor device in accordance with some embodiments.

FIGS. 12-20 are sectional views illustrating another exemplary semiconductor device in accordance with some embodiments.

FIGS. 21-27 are sectional views illustrating another exemplary semiconductor device in accordance with some embodiments.

FIG. 28 is a flow chart for a method forming a vertical structure in accordance with some embodiments.

FIG. 29 is a flow chart for a method forming a vertical structure in accordance with some embodiments.

FIG. 30 is a flow chart for a method forming a vertical structure in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The disclosure describes a method of forming an isolation layer. This disclosure provides at least four types of manufacturing schemes for the isolation layer.

The first includes: deposition of an interlayer dielectric over a vertical structure with a first layer; performing a chemical mechanical polishing (CMP) on the first interlayer dielectric, stopping the CMP on the first layer; and etching back the first interlayer dielectric and the first layer. The second includes: deposition of an interlayer dielectric over a vertical structure with a first layer; performing CMP on the first interlayer dielectric, stopping the CMP on a predetermined height of the first interlayer dielectric; and etching back the first interlayer dielectric and the first layer.

The third includes: deposition of an interlayer dielectric over a vertical structure with a first layer; providing a second layer over the first interlayer dielectric; providing a second interlayer dielectric over the second layer; performing CMP on the first interlayer dielectric, the second layer, and the second interlayer dielectric; stopping the CMP on a lower portion of the second layer; and etching back the first interlayer dielectric and the first layer. The third method may utilize a three layer sandwich structure of ONO (oxide/nitride/oxide layers) to form the first interlayer dielectric, the second layer, and the second interlayer dielectric. The first interlayer dielectric may be formed of, for example, flowable oxide; the second layer may be formed of, for example, SiN, SiON, SiC, SiCN, SiCO, or SiCON; and the second interlayer dielectric may be formed of, for example, plasma enhanced oxide (PE oxide). The second layer may have a thickness of about 5-300 angstroms. The second interlayer dielectric may have a thickness of about 100-3000 angstroms.

The fourth includes: deposition of an interlayer dielectric over a vertical structure with a first layer; performing CMP on the first interlayer dielectric and stopping the CMP on a predetermined height of the first interlayer dielectric; etching back the first interlayer dielectric and the first layer by using gas cluster ion beams; performing wet clean process on the first interlayer dielectric; and etching back the first interlayer dielectric and the first layer by using plasma etching or wet etching. Gas, such as NF₃, SiF₄, CHF₃ and CF₄, may be used in gas cluster ion beams. A post wet clean is an option to reduce defects produced after the process of using gas cluster ion beams.

The abovementioned four methods can be applied to formation of: (1) a bottom isolation layer corresponding to a source of the vertical structure; (2) a middle isolation layer corresponding to a channel of the vertical structure; and (3) a top isolation layer corresponding to a drain of the vertical structure. The methods provide good thickness uniformity of the isolation layers to enhance device performance.

FIG. 1 is a sectional view illustrating an exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 1, a semiconductor device 100 is provided. In the semiconductor device 100, a first vertical structure 110 and a second vertical structure 120 are provided over a substrate 101. The first vertical structure 110 and the second vertical structure 120 may be vertical-gate-all-around devices electrically isolated by shallow trench isolation 102. The first vertical structure 110 may be a PMOS, and may include an n-well 111, a first source 112, a first channel 113, and a first drain 114. The second vertical structure 120 may be an NMOS, and may include a p-well 121, a second source 122, a second channel 123, and a second drain 124. Silicides 115, 116, 125, 126 are used to reduce contact resistance.

The first source 112 is disposed over the n-well 111. The first channel 113 is disposed over the first source 112. The first drain 114 is disposed over the first channel 113. The second source 122 is disposed over the p-well 121. The second channel 123 is disposed over the second source 122. The second drain 124 is disposed over the second channel 123. The following procedures may be performed on the first vertical structure 110 and the second vertical structure 120, so will only be discussed below with respect to the first vertical structure 110.

In one embodiment, the substrate 101 includes a crystalline silicon substrate. In some alternative embodiments, the substrate 101 may be made of some other suitable elemental semiconductor, such as diamond or germanium; a suitable compound semiconductor, such as gallium arsenide, silicon carbide, indium arsenide, or indium phosphide; or a suitable alloy semiconductor, such as silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. Further, the substrate 101 may include an epitaxial layer (epi-layer), may be strained for performance enhancement, and/or may include a silicon-on-insulator (SOI) structure.

FIG. 2 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 2, a first layer 202 is formed over the first vertical structure 110. The first layer 202 may be formed of SiN as an etch stop layer. The first layer 202 may have a thickness of, for example, about 30-300 angstroms. In the embodiment, the first layer 202 is included in the first vertical structure 110. Moreover, a first interlayer dielectric 204 (e.g., an oxide layer) is formed over the first layer 202.

FIG. 3 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 3, a chemical mechanical polishing is performed on the first interlayer dielectric 204 and stops on the first layer 202. Stopping the CMP on the first layer 202 provides good wafer uniformity.

FIG. 4 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 4, the first interlayer dielectric 204 and the first layer 202 are etched back to form the isolation layer 402 corresponding to the source 112 of the first vertical structure 110 by using wet etching or plasma etching. In the embodiment, the isolation layer 402 is aligned to a top surface of the source 112 in conjunction with the channel 113. The method provides good thickness uniformity of the isolation layer 402 among different wafers.

FIG. 5 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 2, as shown in FIG. 5, a chemical mechanical polishing is performed on the first interlayer dielectric 204 and stops on a predetermined thickness 502 (e.g., about 100-1000 angstroms) of the first interlayer dielectric 204 above the first vertical structure 110. In details, the predetermined thickness 502 may be a thickness measured from the first layer 202 above the drain 114 of the first vertical structure 110. Stopping the CMP on the predetermined thickness 502 of the first interlayer dielectric 204 provides good die uniformity.

The chemical polishing process may be configured as follows: polishing down force may be about 0.5-5 psi; table speed may be about 30-110 rpm; slurry type may include colloidal SiO₂, Al₂O₃ or CeO₂ based slurries; and slurry flow rate may be about 50-500 ml/min.

FIG. 6 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 5, as shown in FIG. 6, the first interlayer dielectric 204 and the first layer 202 are etched back to form the isolation layer 602 corresponding to the source 112 of the first vertical structure 110 by using wet etching or plasma etching. In the embodiment, the isolation layer 602 is aligned to a top surface of the source 112 in conjunction with the channel 113. The method provides good thickness uniformity of the isolation layer 602 among different dies.

In some embodiments, before the etch back of the first interlayer dielectric 204 and the first layer 202 by using wet etching or plasma etching, another etch back may be applied to the first interlayer dielectric 204 and the first layer 202 by using gas cluster ion beams.

The gas cluster ion beams may be configured as follows: processing gas may include NF₃, SiF₄, CHF₃, or CF₄; carrier gas may include N₂ or He; the cluster accelerate voltages may be 1 KV-200 KV; the cluster dose may be about 10¹³-10¹⁷ cm²/sec; the cluster flow may be 100-5000 sccm; the pressure may be about 10⁻³-10⁻⁸ torr; the cluster number may be about 100˜50000 molecules; and the cluster size may be about 1-500 nanometers. Gas cluster ion beams may generate an active energy (e.g., 1-3 eV/molecule) for the surfaces of the first interlayer dielectric 204 and the first layer 202, resulting in high temperature (e.g., 10⁴ K) at the surfaces. Gas cluster ion beams heats the processing gas to produce fluorine which reacts with the surfaces to form SiF₄ and O₂, O, NO, NO₂, H₂O, CO, or CO₂ volatile gases.

In some embodiments, a post wet clean is an option to reduce defects produced after the process of using gas cluster ion beams. The wet clean process may use combination of O₃, dilute HF and Ammonia (NH₃) as cleaner for one to five times.

FIG. 7 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 2, as shown in FIG. 7, a second layer 702 is formed over the first interlayer dielectric 204. A second interlayer dielectric 704 is formed over the second layer 702.

The three layer sandwich structure of ONO (oxide/nitride/oxide layers) may be utilized to form the first interlayer dielectric 204, the second layer 702, and the second interlayer dielectric 704. The first interlayer dielectric 204 may be formed of, for example, flowable oxide; the second layer 702 may be formed of, for example, SiN, SiON, SiC, SiCN, SiCO, or SiCON; and the second interlayer dielectric 704 may be formed of, for example, plasma enhanced oxide (PE oxide). The second layer 702 may have a thickness of 5-300 angstroms. The second interlayer dielectric 704 may have a thickness of 100-3000 angstroms.

Moreover, a portion 702 a of the second layer 702 refers to an upper portion which corresponds to protrusion of the first vertical structures 110; the portion 702 b of the second layer 702 refers to a lower portion which corresponds to underlying areas except for the vertical protrusion. Generally, the areas having the protrusion are less than 10% of the entire die so that the portion 702 a of the second layer 702 is more vulnerable to chemical polishing process than is the portion 702 b of the second layer 702.

FIG. 8 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIGS. 7 and 8, a chemical polishing process is performed on the first interlayer dielectric 204, the second layer 702, and the second interlayer dielectric 704, and stops on the lower portion 702 b of the second layer 702.

FIG. 9 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 8, as shown in FIG. 9, the first interlayer dielectric 204 and the first layer 202 are etched back to form the isolation layer 902 corresponding to the source 112 of the first vertical structure 110 by using wet etching or plasma etching. In the embodiment, the isolation layer 902 is aligned to a top surface of the source 112 in conjunction with the channel 113. The method provides good thickness uniformity of the isolation layer 902.

FIG. 10 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 4, as shown in FIG. 10, a high-k dielectric layer 1002, work function metal (WFM) layers 1004, 1006, and a metal gate 1008 are formed over the first vertical structure 110. The processes shown in FIG. 10 may be applied to and continues from FIG. 6 or FIG. 9.

FIG. 11 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 10, as shown in FIG. 11, a portion of the high-k dielectric layer 1002, the work function metal (WFM) layers 1004, 1006, and the metal gate 1008 above the STI 102 between the first vertical structure 110 and second vertical structure 120 are etched back, and the etch-back stops on the isolation layer 402 as a bottom interlayer dielectric.

FIG. 12 is a sectional view illustrating an exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 12, a substrate 1201 having a bottom interlayer dielectric 1202 is provided. A vertical structure 1210 (similar to the first vertical structure 110 in FIG. 11) having a first layer 1212 is provided over the substrate 1201. The first layer 1212 may be, for example, a metal gate. Moreover, a first interlayer dielectric 1204 (e.g., an oxide layer) is formed over the first layer 1212 and the bottom interlayer dielectric 1202.

FIG. 13 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 13, chemical mechanical polishing is performed on the first interlayer dielectric 1204 and stops on the first layer 1212. Stopping the CMP on the first layer 1212 provides good wafer uniformity.

FIG. 14 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 14, the first interlayer dielectric 1204 is etched back to form the isolation layer 1402 corresponding to a channel 1404 of the first vertical structure 1210 by using wet etching or plasma etching. In the embodiment, the isolation layer 1402 is aligned to a top surface of the channel 1404 in conjunction with a drain 1406. The method provides good thickness uniformity of the isolation layer 1402 among different wafers.

FIG. 15 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 12, as shown in FIG. 15, a chemical mechanical polishing is performed on the first interlayer dielectric 1204 and stops on a predetermined thickness 1502 (e.g., about 100-1000 angstroms) of the first interlayer dielectric 1204 above the first vertical structure 1210. In details, the predetermined thickness 1502 may be a thickness measured from the first layer 1212 above a drain 1514 of the first vertical structure 1210. Stopping the CMP on the predetermined thickness 1502 of the first interlayer dielectric 1204 provides good die uniformity.

The chemical polishing process may be configured as follows: polishing down force may be about 0.5-5 psi; table speed may be about 30-110 rpm; slurry type may include colloidal SiO₂, Al₂O₃ or CeO₂ based slurries; and slurry flow rate may be about 50-500 ml/min.

FIG. 16 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 15, as shown in FIG. 16, the first interlayer dielectric 1204 is etched back to form the isolation layer 1602 corresponding to a channel 1604 of the first vertical structure 1210 by using wet etching or plasma etching. In the embodiment, the isolation layer 1402 is aligned to a top surface of a channel 1604 in conjunction with a drain 1606. The method provides good thickness uniformity of the isolation layer 1602 among different dies.

In some embodiments, before the etch back of the first interlayer dielectric 1204 by using wet etching or plasma etching, another etch back may be applied to the first interlayer dielectric 1204 by using gas cluster ion beams.

The gas cluster ion beams may be configured as follows: processing gas may include NF₃, SiF₄, CHF₃, or CF₄; carrier gas may include N₂ or He; the cluster accelerate voltages may be 1 KV-200 KV; the cluster dose may be about 10¹³-10¹⁷ cm²/sec; the cluster flow may be 100-5000 sccm; the pressure may be about 10⁻³-10⁻⁸ torr; the cluster number may be about 100˜50000 molecules; and the cluster size may be about 1-500 nanometers. Gas cluster ion beams may generate an active energy (e.g., 1-3 eV/molecule) for the surfaces of the first interlayer dielectric 1204, resulting in high temperature (e.g., 10⁴ K) at the surfaces. Gas cluster ion beams heats the processing gas to produce fluorine which reacts with the surfaces to form SiF₄ and O₂, O, NO, NO₂, H₂O, CO, or CO₂ volatile gases.

In some embodiments, a post wet clean is an option to reduce defects produced after the process of using gas cluster ion beams. The wet clean process may use combination of O₃ and dilute HF and Ammonia (NH₃) as cleaner for one to five times.

FIG. 17 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 12, as shown in FIG. 17, a second layer 1702 is formed over the first interlayer dielectric 1204. A second interlayer dielectric 1704 is formed over the second layer 1702.

The three layer sandwich structure of ONO (oxide/nitride/oxide layers) may be utilized to form the first interlayer dielectric 1204, the second layer 1702, and the second interlayer dielectric 1704. The first interlayer dielectric 1204 may be formed of, for example, flowable oxide; the second layer 1702 may be formed of, for example, SiN, SiON, SiC, SiCN, SiCO, or SiCON; and the second interlayer dielectric 1704 may be formed of, for example, plasma enhanced oxide (PE oxide). The second layer 1702 may have a thickness of 5-300 angstroms. The second interlayer dielectric 1704 may have a thickness of 100-3000 angstroms.

Moreover, a portion 1702 a of the second layer 1702 refers to an upper portion which corresponds to protrusion of the first vertical structures 1210; the portion 1702 b of the second layer 1702 refers to a lower portion which corresponds to underlying areas except for the vertical protrusion. Generally, the areas having the protrusion are less than 10% of the entire die so that the portion 1702 a of the second layer 1702 is more vulnerable to chemical polishing process than is the portion 1702 b of the second layer 1702.

FIG. 18 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIGS. 17 and 18, a chemical polishing process is performed on the first interlayer dielectric 1204, the second layer 1702, and the second interlayer dielectric 1704, and stops on the lower portion 1702 b of the second layer 1702.

FIG. 19 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 18, as shown in FIG. 19, the first interlayer dielectric 1204 is etched back to form the isolation layer 1902 corresponding to a channel 1904 of the first vertical structure 1210 by using wet etching or plasma etching. In the embodiment, the isolation layer 1902 is aligned to a top surface of a channel 1904 in conjunction with a drain 1906. The method provides good thickness uniformity of the isolation layer 1902.

FIG. 20 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 14, as shown in FIG. 20, a portion of the high-k dielectric layer 2002, work function metal (WFM) layers 2004, 2006, and the first layer 1212 surrounding the drain 1406 of the vertical structure 1210 are etched to expose the drain 1406. The processes shown in FIG. 20 may be applied to and continues from FIG. 16 or FIG. 19. The drain 1406 may include a silicide 2008.

FIG. 21 is a sectional view illustrating an exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 21, a substrate 2101 having a middle interlayer dielectric 2102 is provided. A vertical structure 2110 (similar to the vertical structure 1210 in FIG. 20) having a first layer 2112 is provided over the substrate 2101. The first layer 2112 may be, for example, a silicide. Moreover, a first interlayer dielectric 2104 (e.g., an oxide layer) is formed over the first layer 2112, the vertical structure 2110, and the middle interlayer dielectric 2102.

FIG. 22 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIG. 22, a chemical mechanical polishing is performed on the first interlayer dielectric 2104 and stops on the first layer 2112. The method provides good thickness uniformity of the isolation layer 2202 among different wafers.

FIG. 23 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 21, as shown in FIG. 23, a chemical mechanical polishing is performed on the first interlayer dielectric 2104 and stops on a predetermined thickness 2302 (e.g., 100-1000 angstroms) of the first interlayer dielectric 2104 above the first vertical structure 2110. In details, the predetermined thickness 2302 may be a thickness measured from the first layer 2112 of the first vertical structure 2110. Stopping the CMP on the predetermined thickness 2302 of the first interlayer dielectric 2104 provides good die uniformity.

The chemical polishing process may be configured as follows: polishing down force may be about 0.5-5 psi; table speed may be about 30-110 rpm; slurry type may include colloidal SiO₂, Al₂O₃ or CeO₂ based slurries; and slurry flow rate may be about 50-500 ml/min.

FIG. 24 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 23, as shown in FIG. 24, the first interlayer dielectric 2104 is etched back to form the isolation layer 2402 corresponding to a drain 2404 of the first vertical structure 2110 by using wet etching or plasma etching. The method provides good thickness uniformity of the isolation layer 2402 among different dies. The drain 2404 may include the first layer 2112 (made of silicide).

In some embodiments, before the etch back of the first interlayer dielectric 2104 by using wet etching or plasma etching, another etch back may be applied to the first interlayer dielectric 2104 by using gas cluster ion beams.

The gas cluster ion beams may be configured as follows: processing gas may include NF₃, SiF₄, CHF₃, or CF₄; carrier gas may include N₂ or He; the cluster accelerate voltages may be about 1 KV-200 KV; the cluster dose may be about 10¹³-10¹⁷ cm²/sec; the cluster flow may be about 100-5000 sccm; the pressure may be about 10⁻³-10⁻⁸ torr; the cluster number may be about 100-50000 molecules; and the cluster size may be about 1-500 nanometers. Gas cluster ion beams may generate an active energy (e.g., 1-3 eV/molecule) for the surfaces of the first interlayer dielectric 2104, resulting in high temperature (e.g., 10⁴ K) at the surfaces. Gas cluster ion beams heats the processing gas to produce fluorine which reacts with the surfaces to form SiF₄ and O₂, O, NO, NO₂, H₂O, CO, or CO₂ volatile gases.

In some embodiments, a post wet clean is an option to reduce defects produced after the process of using gas cluster ion beams. The wet clean process may use combination of O₃ and dilute HF and Ammonia (NH₃) as cleaner for one to five times.

FIG. 25 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 21, as shown in FIG. 25, a second layer 2502 is formed over the first interlayer dielectric 2104. A second interlayer dielectric 2504 is formed over the second layer 2502.

The three layer sandwich structure of ONO (oxide/nitride/oxide layers) may be utilized to form the first interlayer dielectric 2104, the second layer 2502, and the second interlayer dielectric 2504. The first interlayer dielectric 2104 may be formed of, for example, flowable oxide; the second layer 2502 may be formed of, for example, SiN, SiON, SiC, SiCN, SiCO, or SiCON; and the second interlayer dielectric 2504 may be formed of, for example, plasma enhanced oxide (PE oxide). The second layer 2502 may have a thickness of about 5-300 angstroms. The second interlayer dielectric 2504 may have a thickness of about 100-3000 angstroms.

Moreover, a portion 2502 a of the second layer 2502 refers to an upper portion which corresponds to protrusion of the first vertical structures 2110; the portion 2502 b of the second layer 2502 refers to a lower portion which corresponds to underlying areas except for the vertical protrusion. Generally, the areas having the protrusion are less than 10% of the entire die so that the portion 2502 a of the second layer 2502 is more vulnerable to chemical polishing process than is the portion 2502 b of the second layer 2502.

FIG. 26 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. As shown in FIGS. 25 and 26, a chemical polishing process is performed on the first interlayer dielectric 2104, the second layer 2502, and the second interlayer dielectric 2504, and stops on the lower portion 2502 b of the second layer 2502.

FIG. 27 is a sectional view illustrating the exemplary semiconductor device in accordance with some embodiments. Continuing from FIG. 26, as shown in FIG. 27, the first interlayer dielectric 2104 is etched back to form the isolation layer 2702 corresponding to a drain 2704 of the first vertical structure 2110 by using wet etching or plasma etching. The method provides good thickness uniformity of the isolation layer 2702. The drain 2704 may include the first layer 2112 (made of silicide).

FIG. 28 is a flow chart for a method of forming a vertical structure. As shown in FIG. 28, a method 2800 is provided. The method 2800 includes the following operations: providing a substrate (2802); providing a vertical structure having a first layer over the substrate (2804); providing a first interlayer dielectric over the first layer (2806); performing CMP on the first interlayer dielectric (2808); and etching back the first interlayer dielectric and the first layer to form the isolation layer corresponding to a source of the vertical structure (2810).

The operation 2804 may further include providing the vertical structure having the first layer made of SiN as an etch stop layer over the substrate. The method 2800 may further include stopping the CMP on the first layer. The method 2800 may further include stopping the CMP on a predetermined thickness of the first interlayer dielectric above the vertical structure. The operation 2804 may further include etching back the first interlayer dielectric and the first layer by using wet etching or plasma etching. The method 2800 may further include etching back the first interlayer dielectric and the first layer by using gas cluster ion beams. The method 2800 may further include: providing a second layer over the first interlayer dielectric; providing a second interlayer dielectric over the second layer; performing CMP on the first interlayer dielectric, the second layer, and the second interlayer dielectric; and stopping the CMP on a lower portion of the second layer.

FIG. 29 is a flow chart for a method of forming a vertical structure. As shown in FIG. 29, a method 2900 is provided. The method 2900 includes the following operations: providing a substrate having a bottom interlayer dielectric (2902); providing a vertical structure having a first layer over the substrate (2904); providing a first interlayer dielectric over the first layer and the bottom interlayer dielectric (2906); performing CMP on the first interlayer dielectric (2908); and etching back the first interlayer dielectric to form the isolation layer corresponding to a channel of the vertical structure (2910).

The operation 2904 may further include providing the vertical structure having the first layer made of metal gate as an etch stop layer over the substrate. The method 2900 may further include stopping the CMP on the first layer. The method 2900 may further include stopping the CMP on a predetermined thickness of the first interlayer dielectric above the vertical structure. The operation 2910 may further include etching back the first interlayer dielectric by using wet etching or plasma etching. The method 2900 may further include etching back the first interlayer dielectric and the first layer by using gas cluster ion beams. The method 2900 may further include: providing a second layer over the first interlayer dielectric; providing a second interlayer dielectric over the second layer; performing CMP on the first interlayer dielectric, the second layer, and the second interlayer dielectric; and stopping the CMP on a lower portion of the second layer.

FIG. 30 is a flow chart for a method of forming a vertical structure. As shown in FIG. 30, a method 3000 is provided. The method 3000 includes the following operations: providing a substrate having a middle interlayer dielectric (3002); providing a vertical structure having a first layer over the substrate (3004); providing a first interlayer dielectric over the first layer and the middle interlayer dielectric (3006); performing CMP on the first interlayer dielectric (3008); and etching back the first interlayer dielectric to form the isolation layer corresponding to a drain of the vertical structure (3010).

The operation 3004 may further include providing the vertical structure having the first layer made of silicide as an etch stop layer over the substrate. The method 3000 may further include stopping the CMP on the first layer. The method 3000 may further include stopping the CMP on a predetermined thickness of the first interlayer dielectric above the vertical structure. The method 3000 may further include etching back the first interlayer dielectric by using gas cluster ion beams. The method 3000 may further include: providing a second layer over the first interlayer dielectric; providing a second interlayer dielectric over the second layer; performing CMP on the first interlayer dielectric, the second layer, and the second interlayer dielectric; and stopping the CMP on a lower portion of the second layer.

According to an exemplary embodiment, a method of forming an isolation layer is provided. The method includes the following operations: providing a substrate; providing a vertical structure having a first layer over the substrate; providing a first interlayer dielectric over the first layer; performing CMP on the first interlayer dielectric; and etching back the first interlayer dielectric and the first layer to form the isolation layer corresponding to a source of the vertical structure.

According to an exemplary embodiment, a method of forming an isolation layer is provided. The method includes the following operations: providing a substrate having a bottom interlayer dielectric; providing a vertical structure having a first layer over the substrate; providing a first interlayer dielectric over the first layer and the bottom interlayer dielectric; performing CMP on the first interlayer dielectric; and etching back the first interlayer dielectric to form the isolation layer corresponding to a channel of the vertical structure.

According to an exemplary embodiment, a method of forming an isolation layer is provided. The method includes the following operations: providing a substrate having a middle interlayer dielectric; providing a vertical structure having a first layer over the substrate; providing a first interlayer dielectric over the first layer and the middle interlayer dielectric; performing CMP on the first interlayer dielectric; and etching back the first interlayer dielectric to form the isolation layer corresponding to a drain of the vertical structure.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of forming an isolation layer, comprising: providing a shallow trench isolation; providing a vertical structure that includes a source region, a channel region over the source region, a drain region over the channel region, and a gate structure surrounding the channel region, wherein the source region is embedded in a first interlayer dielectric (ILD) layer, and the channel region and the gate structure is embedded in a second ILD layer disposed over the first ILD layer, the drain region protrudes from the second ILD layer; forming a third ILD layer over the drain region and the second ID layer, the third ILD layer being in contact with the drain region; and performing CMP on the third ILD layer; and stopping the CMP upon reaching an uppermost portion of the vertical structure, the first LD layer includes an etch stop layer formed on the source region and the shallow trench isolation and a bottom ILD layer disposed on the etch stop layer.
 2. The method of claim 1, wherein: the vertical structure further a silicide layer disposed on the drain regions, and the CMP stops on the silicide layer.
 3. The method of claim 1, wherein the first ILD layer is formed by: forming a layer for the etch stop layer over the vertical structure, the layer including: a horizontal upper portion overlying a top of the vertical structure, a horizontal bottom portion overlying the shallow trench isolation, and a vertical side portion extending downward from the upper portion and in overlying contact with a side of the source, channel and drain regions; providing a dielectric layer for the bottom ILD layer over the etch stop layer's upper, bottom and side portions; performing CMP on the dielectric layer, and stopping the CMP upon reaching a top of the etch stop layer's upper portion; and etching back the dielectric layer and the etch stop layer's side portion, thereby exposing the side of the channel and the drain.
 4. The method of claim 3, wherein during the etching back the dielectric layer, the dielectric layer and the etch stop layer's side portion are etched together.
 5. The method of claim 3, wherein the etch stop layer is made of SiN.
 6. The method of claim 3, wherein the silicide layer is formed on the drain region formed before the etch stop layer is formed.
 7. The method of claim 6, wherein: the silicide layer has a top surface and a side, and the etch stop layer is provided such that the vertical side portion is in overlying contact with the side of the silicide layer.
 8. The method of claim 1, wherein the second ILD layer is formed by: forming a gate dielectric layer over the channel region and the drain region and on the etch stop layer and the first layer; forming one or more conductive layers over the gate dielectric layer; providing a dielectric layer for the second ILD layer over the one or more conductive layers; performing CMP on the dielectric layer for the second ILD layer, and stopping the CMP upon reaching an uppermost layer of the one or more conductive layers; and etching back the dielectric layer for the second ILD layer to a level corresponding to the channel region.
 9. The method of claim 8, wherein the etching back comprises one of wet etching, plasma etching or gas cluster ion beams.
 10. The method of claim 9, wherein: each of the gate dielectric layer and the one or more conductive layer includes a lower horizontal portion that projects horizontally away from a bottom end of the respective vertical portion, and the method further comprises etching away a distal section of each of the lower horizontal portions, thereby shortening each of the lower horizontal portions.
 11. The method of claim 8, wherein the gate dielectric layer includes a high-k dielectric layer.
 12. The method of claim 11, wherein the one or more conductive layer includes at least one work function metal (WFM) layer.
 13. A method of forming an isolation layer, comprising: providing a shallow trench isolation; providing a vertical structure that includes a source region, a channel region over the source region, a drain region over the channel region, and a gate structure surrounding the channel region, wherein the source region is embedded in a first interlayer dielectric (ILD) layer, and the channel region and the gate structure is embedded in a second ILD layer disposed over the first ILD layer, the drain region protrudes from the second ILD layer; forming a third ID layer over the drain region and the second ILD layer, the third ILD layer including a top layer, a middle layer and a bottom layer; performing first CMP on the third ILD layer, and stopping the first CMP so that part of the middle layer remains; and performing second CMP to remove the part of the middle layer and the bottom layer, and stopping the second CMP upon reaching an uppermost portion of the vertical structure, wherein the top layer is fully removed in the first CMP and the middle layer is fully removed in the second CMP.
 14. The method of claim 13, wherein: the vertical structure further a silicide layer disposed on the drain regions, and the second CMP stops on the silicide layer.
 15. The method of claim 13, wherein the middle layer includes at least one selected from the group consisting of SiN, SiON, SiC, SiCN, SiCO and SiCON.
 16. The method of claim 15, if wherein a thickness of the middle layer is in a range from 0.5 nm to 30 nm and a thickness of the top layer is in a range from 10 nm to 300 nm.
 17. The method of claim 13, wherein the middle layer includes SiCON.
 18. A method of forming an isolation layer, comprising: providing a shallow trench isolation; providing a vertical structure that includes a source region, a channel region over the source region, a drain region over the channel region, and a gate structure surrounding the channel region, wherein the source region is embedded in a first interlayer dielectric (ILD) layer, and the channel region and the gate structure is embedded in a second ILD layer disposed over the first ILD layer, the drain region protrudes from the second ILD layer; forming a third ILD layer over the drain region and the second ILD layer, third ILD layer being in contact with the drain region; performing CMP on the third ILD layer, and stopping the CMP before reaching an uppermost part of the vertical structure, thereby leaving a remaining layer of the third ILD layer above the uppermost part of the vertical structure; and etching back the third ILD layer with the remaining layer to a level corresponding to the uppermost part of the vertical structure, wherein a thickness of the remaining layer of the third ILD layer from the highest portion is in a range from 10 nm to 100 nm.
 19. The method of claim 18, wherein: the vertical structure further a silicide layer disposed on the drain regions, and the uppermost part of the vertical structure is an upper surface of the silicide layer.
 20. The method of claim 18, further comprising providing a shallow trench isolation, wherein the second ILD layer are provide on the shallow trench isolation. 